Diseases of the vascular system afflict a substantial portion of the adult population. Many of these diseases are life-threatening conditions that demand substantial surgical intervention. For example, an aortic aneurysm is a particularly troubling medical condition in which a localized abnormal dilation of the aorta occurs. At the site of the dilation the aorta wall becomes thin and weak, giving rise to a substantial danger of rupture and death by internal hemorrhaging. Although there are traditional surgical procedures that can be effective in treating conditions like an aortic aneurysm, the surgery itself can be taxing and dangerous for the patient. In particular, for an aortic aneurysm the surgical procedure requires that the patient's abdominal cavity be opened to reach and expose the aortic aneurysm. The patient is maintained on an independent life support system while the aneurysm is incised lengthwise to enable insertion of a vascular graft into the aorta that spans the weakened section of the aorta to carry blood between the remaining healthy portions. This is a highly invasive and dangerous surgical procedure that requires that the surgeon balance the patient's risk of harm from the aneurysm against the patient's risk of harm from the treatment. Today, approximately 50,000 abdominal aortic aneurysms are surgically repaired annually in the United States. However, more aneurysms are left untreated than treated as much of the afflicted population is ill or frail and therefore unlikely to survive the surgery.
To reduce the mortality and morbidity resulting from these highly invasive surgical procedures, and to provide surgical treatments suitable for treating a broad range of patients, catheter delivery systems have been developed that allow a vascular graft to be inserted within the patient's vascular system through a small incision made within a peripheral artery of the patient. The catheter is fed through the patient's artery and to the sight of the diseased or compromised vascular tissue. A graft is then passed through an interior channel of the catheter and disposed within the patient's vascular system to support, or supplant, the diseased tissue. Typically, the graft is an implantable endovascular stent-graft that is tubular in shape and that is adapted to act as a prosthetic artery for removing pressure from the weakened aortic wall. Upon delivery of the graft, the catheter is removed from the patient's vascular system and the small incision is closed. Accordingly, these systems for the transluminal delivery of endovascular grafts bypass the need for highly invasive surgical procedures, such as abdominal surgery, by allowing a doctor to use the patient's natural body lumens as-pathways for reaching the diseased tissue within the vascular system.
Today, there are a variety of existing transluminal delivery systems and endovascular grafts for treating vascular conditions such as aortic aneurysms. One class of these systems is directed to the treatment of abdominal aortic aneurysms that are proximate or extend into the iliac arteries. These systems provide for the delivery of a bifurcated endovascular graft that includes a main body that attaches within the descending aorta and a bifurcated portion that includes two legs, each of which is an endovascular graft, and each of which couples to the main body and carries blood to a respective one of the iliac arteries.
In some systems, the bifurcated graft is a single unit that includes the main body and two legs. In these systems, the treating surgeon uses one or more catheters to deliver the graft to the site of the aneurysm and in a cumbersome process the surgeon releases the graft from the catheters and arranges the main body of the graft within the aorta and the legs within the two iliac arteries. As an alternative to this cumbersome process, biomedical engineers have developed modular endovascular grafts that include a main body and one or more separate leg grafts. These modular designs eliminate the need for the surgeon to arrange the graft within the patient's aneurysm. Instead, the surgeon forms the graft by transluminally delivering each piece of the graft in such a way that during each subsequent delivery, a new piece is aligned and positioned to join with the previously delivered pieces and to form the complete endovascular graft.
Although these modular endovascular grafts can provide an effective treatment, their application is generally limited to aneurysms that occur within aortas that are substantially straight and only moderately transverse to the patient's iliac arteries. In part, this is because the process of assembling the modular graft requires that the pieces be readily and precisely aligned and positioned during delivery. However, an unfortunate side effect of some vascular diseases, including aneurysms, is that tissue growth can occur at the site of the diseased vessel. This can cause the diseased aorta to lengthen. Due to its confinement within the abdominal cavity, the lengthening aorta often twists and loops into a torturous configuration. For several reasons, patients with twisted aortas are often poor candidates for receiving modular endovascular grafts through transluminal delivery. For example, it may be difficult for the surgeon to achieve the necessary alignment for delivering the different pieces of the modular endovascular graft. Further, the twisted aorta often has only a short renal neck of healthy tissue to which the main body of the graft may attach. Therefore, the surgeon may only be able to place a limited portion of the main graft body into the short renal neck, leaving a large section of the graft to extend into the aneurysm at an angle that can be significantly transverse to the iliac arteries through which the delivery catheter travels. In these cases, it may not be possible for the surgeon to snake the guidewire that is used to deliver the other components of the modular graft through the iliac artery and into the portion of the modular endovascular graft that extends into the aneurysm. Consequently, for many of these patients, the only viable solution is to have abdominal surgery and to incise the compromised aortic tissue and supplant this tissue with a vascular graft.
Accordingly, it would be desirable to provide endoprosthetic implants, including modular endovascular grafts, that are suited for disposition within body lumens, including short or torturous body lumens, to thereby provide a minimally invasive surgical procedure suitable for application in a broad class of vessels.